Password Enabled Public-Key Infrastructure (PKI): Virtual Smartcards vs. Virtual Soft Tokens

1. Password Enabled Public-Key Infrastructure (PKI):Virtual Smartcards vs. Virtual Soft Tokens Ravi Sandhu Chief Scientist SingleSignOn.Net & Professor, George Mason University Mihir Bellare Chief Cryptographer SingleSignOn.Net & Professor, Univ. of California--San Diego Ravi Ganesan Chief Executive Officer SingleSignOn.Net 11417 Sunset Hills Rd., Reston, VA 20190

2. Why Password-Enabled PKI • Smartcards have not happened • It’s the smartcard readers stupid! • Roaming capability is critical • Even DoD is stretched in large-scale deployment • Trends are not in favor of smartcards • Deployment scale of 10’s or even 100’s of millions of users • Computing devices are proliferating • Large installed base of reader-less computers Smartcards are likely to remain a high-assurance niche application

3. Solve PKI Gap and Silo Problem • Result • Phased migration path • No “quantum jump” • PKI integral, not silo’d Strong PKI Systems PKI with Password Convenience Password Usability PKI Capability PKI Hardened Passwords No change for users No change for issuer Eliminate weaknesses Weak Password Systems

4. A Common Misperception • Fact: Password based systems are often vulnerable to attacks • Myth: Passwords are inherently insecure. • Fact: It is completely possible to design a sufficiently secure password system. Designing sufficiently secure password-based systems is non-trivial but it is possible.

5. Another Common Misperception • Fact: Users hate current password systems that require • too many passwords and • force too many changes • Myth: Users inherently hate passwords. • Fact: It is completely possible to design a user friendly password system with PKI-enabled Single Sign On. Designing user-friendly and sufficiently secure password-enabled PKI systems is non-trivial but it is possible.

6. Password Vulnerabilities and Counter-Measures • Bad password selection • enforce complexity rules • On-line guessing attack • throttling mechanism • Off-line guessing (dictionary attacks) • don’t reveal required information (we know how to design such protocols) • Undetected theft and sharing • online intrusion detection to discover • deter sharing, e.g., sharing reveals sensitive user information • Use of same password at strong and weak servers • user awareness and education • Password reuse • don’t force unnecessary password changes • Server spoofing • use secure protocols to prove knowledge of password w/o sending it • limit password exposure to trusted servers • Server compromise • use hardened servers or multiple servers

7. Password Benefits • Instant roaming capability • Proven user acceptance • 100’s of millions of passwords usages per day in cyberspace • Cheap • Self-maintained • Password resets • Password change

8. Traditional Public-Key Infrastructure (PKI) • How to distribute public-keys • Digital Certificates • Certificate Revocation Lists • How to distribute private-keys (long-term) • Smartcards • The private key never leaves the smartcard • Often called a hard token • How to distribute private-keys (short-term) • Password protected on the hard disk • Not very mobile • Password protected on a floppy disk • Often called a soft token

9. “Modern” Public-Key Infrastructure (PKI) • How to distribute public-keys • Digital Certificates • Certificate Revocation Lists • On-line servers for certificate validation • How to distribute private-keys (long-term) • Smartcards • The private key never leaves the smartcard • Often called a hard token • How to distribute private-keys (short-term) • Password protected on the hard disk • Not very mobile • Password protected on a floppy disk • Often called a soft token • On-line servers for password-enabled mobility

10. Approaches How to marry PKI and Passwords? • Approach 1: Virtual Soft Token Use password to encrypt private key and store it on remote server(s). Need password to RETREIVE private key. • Approach 2: Virtual Smartcard The password is part of the composite private key. Need password to USE private key.

11. Trivial Insecure Virtual Soft Token • Private key encrypted with user’s password is stored on an on-line server Epwd(private-key) • Anyone is allowed to retrieve the encrypted private key • Only the user can decrypt it using the password • Unacceptable risk due to dictionary attack

12. Cryptographic Camouflage, Hoover and Kausik • Epwd(private-key) • Dictionary attack • Knowledge of public key allows attacker to obtain known plaintext • So prohibit knowledge of public key resulting in closed public-key system

13. EKE Roaming, Bellovin-Merritt et al • Store Epwd(private-key) on server • Transmit EK(Epwd(private-key)) where K is a strong symmetric key • K is established using password-based authenticated key exchange protocol (such as EKE or SPEKE) • Immune to off-line dictionary attack

14. Hardened Password Roaming, Kaliski-Ford • User’s “hardened password” is retrieved at any computer from two on-line servers • Compromise of both servers is required to compromise “hardened password” • Successful retrieval of “hardened password” requires knowledge of user’s password • User’s private key is retrieved by means of “hardened password” • Once retrieved the user’s private key can be freely used on this computer

15. Credential Servers 1 & 2 Alice knows Password,Pa Step 5: Ask for Credentials Step 1: Alice sends Pa Long term private key is locked with ‘hardened password’ H. Need duplicate credentials server for redundancy. Client Computer Step 2: Client Computer starts process Step 6: Check if Cert is revoked Step 7: Return Cert and H (D) Step 3: Get H1 Security Servers 1 & 2 Step 4: GetH2 Step 9: Finally get around to logon or sign operation! Revocation Servers 1 & 2 Security server with partial knowledge of ‘H’ (H1). Need duplicate server for redundancy. Security Servers 3 & 4 OCSP server to check for revocation Security server with remaining knowledge of ‘H’ (H2). Need duplicate server for redundancy. Step 8: UseH to decrypt private key D

16. Approaches How to marry PKI and Passwords? • Approach 1: Virtual Soft Token Use password to encrypt private key and store it on remote server(s). Need password to RETREIVE private key. • Approach 2: Virtual Smartcard The password is part of the composite private key. Need password to USE private key.

17. Trivial Insecure Virtual Smart Card • Keep the private key on an on-line server • Use the password as authentication to enable use of the private key on the server • Lose non-repudiation

18. M A A M M And creates A A A ID: Castle Corp FN: Castle LN: Corp . . • Alice takes M M And creates CC • But (presto!) !!! M CA M = A A A We want: • Appliance takes

19. Password M • Alice has password P which ONLY she knows. Password P expands to key d1 on computer. CA A A ID: Castle Corp FN: Castle LN: Corp . . • A Secure Identity Appliance has key d2 for Alice which ONLY it knows. • As before, Alice has public cert, with public key e, signed by a CA. CC CA A A Secure Identity Appliance The Practical PKITM Approach • Process • Alice authenticates to appliance, sets up secure channel and sends M. • Appliance performs partial signature on M with its key for Alice d2. • Alice completes signature with her key d1.

20. Comparison • Practical PKITM • Keys: • Alice Public = e • Alice PKCS5(password, salt, iteration count) = d1 • Alice Cert = C • Alice appliance key = d2 • Signing: • Alice logs on to appliance using d1 and creates secure channel • Spartial = Sign(M,d2) • S = Sign(Spartial,d1) • Send [S, C] to Bob • Bob: • Gets e from C • Does Verify(S,e) = M? Traditional PKI Keys: • Alice Public = e • Alice Private = d • Alice Cert = C Signing: a) S = Sign (M,d) Send [S, C] to Bob Bob: Gets e from C Does Verify(S,e) = M?

21. Difference #1: Alice has short convenient password Difference #2: Alice has to interact with appliance to sign. Comparison • Practical PKITM • Keys: • Alice Public = e • Alice PKCS5(password, salt, iteration count) = d1 • Alice Cert = C • Alice appliance key = d2 • Signing: • Alice logs on to appliance using d1 and creates secure channel • Spartial = Sign(M,d2) • S = Sign(Spartial,d1) • Send [S, C] to Bob • Bob: • Gets e from C • Does Verify(S,e) = M? Traditional PKI Keys: • Alice Public = e • Alice Private = d • Alice Cert = C Signing: a) S = Sign (M,d) Send [S, C] to Bob Bob: Gets e from C Does Verify(S,e) = M?

22. NOTHING ELSE CHANGES!!!! Comparison • Practical PKITM • Keys: • Alice Public = e • Alice PKCS5(password, salt, iteration count) = d1 • Alice Cert = C • Alice appliance key = d2 • Signing: • Alice logs on to appliance using d1 and creates secure channel • Spartial = Sign(M,d2) • S = Sign(Spartial,d1) • Send [S, C] to Bob • Bob: • Gets e from C • Does Verify(S,e) = M? Traditional PKI Keys: • Alice Public = e • Alice Private = d • Alice Cert = C Signing: a) S = Sign (M,d) Send [S, C] to Bob Bob: Gets e from C Does Verify(S,e) = M?

23. A Velocity Checking Easy to report ID: Alice FN: Alice LN: Smith Email:alice@cc.com . . CA CA ID stolen Theft detected Theft reported CA revokes ID Recipient (we hope) stops accepting ID Strong Fraud Management ID CANNOT BE USED ANY FURTHER! INSTANT, COMPLETE, REVOCATION

24. Every signature requires appliance interaction. So appliance logs can be used for velocity checking. Every signature requires appliance interaction. Once revoked key cannot be used further! Instant, complete revocation! Consumer or CSR can use password to revoke instantly! A Velocity Checking Easy to report ID: Alice FN: Alice LN: Smith Email:alice@cc.com . . CA CA ID stolen Theft detected Theft reported CA revokes ID Recipient (we hope) stops accepting ID Strong Fraud Management ID CANNOT BE USED ANY FURTHER! INSTANT, COMPLETE, REVOCATION

25. SingleSignOn.Net • Practical PKITM solution • Ease of use: password based • Quick to deploy • Simple to manage with least privilege • Velocity checking and instant revocation • Reusable for multiple applications • Web, Wireless, VPN, email, etc. • Use existing standards and widely deployed technologies

26. Summary • Password enabled solutions are poised to jump start the stalled PKI car. • Major vendors jumping into password enabled solutions using on-line servers is a good sign. • “Many servers” are not all good, and have quality/security downside. • Making password a part of the composite private key (virtual smartcards) provides substantial advantages over using password to retrieve private key (virtual soft tokens).